1. Field of the Invention
The invention relates to multiple-lite insulated glazing units. More particularly, the invention relates to multiple-lite insulated glazing units containing a light dispersive film, such as a film having a hologram, diffraction grating or light refracting pattern thereon.
2. Description of the Prior Art
Over the last two decades, there has been an increased emphasis on the use of multiple-lite insulated glazing units in architectural design. One of the primary motivations behind this increased emphasis has been the advent of numerous governmental regulations which mandate the installation of such constructions due to their high energy efficiency. At the same time, rising energy prices have made the high cost of such multiple-lite glazing units, when compared to conventional single-lite glazing units, a prudent long-term investment.
The conventional multiple-lite insulated glazing unit has traditionally employed two or more lites of glass, the faces of which were in a parallel, spaced relationship. This spaced relationship provided one or more dead air spaces between the lites which, in turn, imparted insulating properties to the structure. In the most common arrangement, two parallel lites of glass were held in a spaced relationship by a metallic or plastic standard glazing frame positioned around the perimeter of the lites. When a triple-lite glazing unit was desired for more energy efficiency, one common approach was to use three parallel lites of glass. However, this structure can be extremely heavy.
In an attempt to reduce this weight detriment, while at the same time maintaining the improved energy efficiency of the triple-lite construction, a triple-lite glazing unit was developed which employed two glass lites and an intermediate plastic film interposed between the glazing lites in a parallel, spaced relationship as described in U.S. Pat. No. 4,335,166 and U.S. Pat. No. 4,853,264, both of which are incorporated herein by reference. In a further attempt to exploit the energy efficiency of such a unit, it has been suggested to coat the intermediate plastic film with a material, such as metal, which is highly reflective of long wave infrared radiation. These coatings are typically referred to as heat reflective coatings.
In no instance has the intermediate plastic film been used to disperse visible light into its constituent frequencies by diffraction and/or refraction, nor has a holographic pattern been incorporated into the intermediate plastic film. In fact, one of the prime objectives of these prior art insulated glazing units has been to prevent dispersion of visible light, light dispersion being generally considered deleterious to the desired function of the device.
If architectural designers or artists desired to disperse visible light by diffraction or refraction in connection with an insulated glazing unit, it was known by those skilled in the art that a transparent film etched with a holographic pattern or containing a diffraction grating could be laminated to one of the outer surfaces of the glazing lites. However, as such a construction was generally considered unsatisfactory, there has been a tendency to stay away from the application of light dispersive films to insulated glazing units. This construction was generally considered inadequate due to the recognized potential for bubbling, warping, and peeling of the film, which would result from the failure of the film to adhere to the lites after repeated thermal expansion and contraction cycles and exposure of the film to moisture. The above construction was also avoided due to the knowledge that prolonged exposure of the polyester film, which is typically used in the construction of transparent holographic films and diffraction gratings, to UV light would cause the film to become brittle and peel or crack. The exposed polyester film would also be susceptible to being marred and scratched, thereby degrading the holographic image or diffraction grating contained on the film. Accordingly, a need exists for an insulated glazing unit capable of dispersing light, but which eliminates or reduces the foregoing problems.